As disclosed in U.S. Pat. No. 4,594,453 (Ranken et al.), it is known that various ar-(hydrocarbylthio)aromatic amines are useful as intermediates in the preparation of biologically-active materials, polyurethanes, etc., and that they can be prepared by reacting appropriate aromatic amines with hydrocarbyl disulfides in the presence of suitable catalysts, such as aluminum chloride. Unfortunately, these syntheses typically result in the formation of mixtures of ar-(hydrocarbylthio)aromatic amines.
U.S. Pat. No. 4,547,593 (Ranken) teaches that particular (hydrocarbylthio)phenols can be prepared by heating other (hydrocarbylthio)phenols in the presence of an aluminum phenoxide catalyst to redistribute the hydrocarbylthio groups.
Fujisawa et al., Bulletin of the Chemical Society of Japan, Vol. 43, No. 4, 1970, pp. 1189-1196, teach that arylthio substituents in o-, m-, and p-tolyl phenyl sulfides can be rearranged in the presence of aluminum chloride. Han et al., Tetrahedron Letters, No. 30, pp. 2629-2632, 1970, also teach that arylthio substituents in aromatic hydrocarbons can be rearranged with aluminum chloride, presumably by sulfonium ion formation, ring thiation, and subsequent proton loss.
The redistribution of hydrocarbylthio groups on an aromatic ring containing an amino group, however, is not expected. March, Advanced Organic Chemistry, Second Edition, McGraw-Hill, New York, page 486, teaches that amino groups are very reactive toward Lewis acids such as aluminum bromide and aluminum chloride. Their presence on an aromatic ring inhibits the catalytic activity that the Lewis acid would otherwise have in electrophilic aromatic substitution reactions such as Friedel-Craft alkylations. The inhibition of the catalytic activity of the Lewis acids by the amino group, particularly when ether and sulfides are involved, is due to the strong complexation of the amino group with the Lewis acid. Oae, Organic Chemistry of Sulfur, Plenum Press, New York, page 251, teaches that the order of bond strength for the complexation of compounds with an aluminum halide is amines&gt;ethers&gt;sulfides. The reaction of (hydrocarbylthio)aromatic amines with aluminum chloride would thus be expected to give products involving the nitrogen rather than the sulfur. Typical reactions would be the formation of diarylamines as taught by Thomas, Anhydrous Aluminum Chloride in Organic Chemistry, Reinhold Publishing Corporation, New York, pp. 156-157, 1941.